German Patent Application DE 39 07 730 A1, incorporated herein by reference, describes a method and an apparatus for carrying out a method for grinding the working rolls of a planetary rolling mill, in which the entire set of rolls of the planetary mill is ground in with special grinding machine, without dismounting the working rolls.
There are generally a set of 24 working rolls associated with each of the planetary rolls, which must be reground after approximately every eight hours of use, because their surfaces become worn. Therefore, it may be appreciated that DE 36 07 730 A1 provides a considerable advantage and improvement over an earlier method for grinding the working rolls, consisting of removing the working rolls from the set of planetary rolls individually by hand, in the workshop or mill, and installing new ones. Particularly in the case of large machines of, for instance, strip width of about 1300 mm, this method is cumbersome, time-consuming and very expensive. However, the solution proposed in DE 39 07 730 A1, even though it constitutes a substantial simplification and improvement, as well as saving time in the regrinding process as compared with the traditional methods, has various problems, which result from the fact that the alignment of the planet rolls in a turning device, intended for the machining of the working rolls while in the installed condition, is very difficult. The precision of the grinding of the working rolls depends directly on the alignment of the planet rolls, therefore any imprecision in alignment or any misalignment will result in imprecise grinding, and thus the planetary mill using these rolls will not operate with greatest effectiveness.
Another disadvantage of the known apparatus for the grinding of working rolls consists of the high investment expenses for the equipment necessary for changing the various rolls. In particular, in the prior art method, at least three sets of rolls are required, each set of rolls consisting of two planet rolls having the support bodies, intermediate rolls and working rolls. The three sets of rolls required are a first set for rolling in the mill, a second set which is in the shop for regrinding of the working rolls, and a spare third set.